Sink float method of classifying wet flocculated solid particles



United States Patent ()fiice 3,13%,946 Patented Mar. 14,1967

SINK FLQAT METHOD F CLASSIFYING WET FLOCULATED SQLID EARTIQLES AbrahamMite ranger, Kiriat Bialilr, and Joseph Mizrahi, Kiriat Hahn, Ksraei,assignors, by mesne assignments, to Israel Mining Industriee-lnstitutefor Research and Development, a company of lsraei No Drawing. Filed Nov.5, 1963, Ser. No. 321,399 Claims priority, application Israel, Dec. 24,1962, 13,443/62 8 (Iiaims. (Ci. 269-) The present'invention concerns thesink-float classification of granular solid materials.

It is known that when a ground dry ore composed, for example, of twominerals of different specific gravities is dispersed in awater-immiscible organic liquid of a specific gravity intermediatebetween those of the two minerals and the dispersion is allowed tosettle, the minerals separate into a heavier'fraction which sinks to thebottom, and a lighter fraction which floats. If, however, the solidmaterial is wetted with water or an aqueous liquor, some of the lightand heavy particles flocculate in common and their separation in theaforesaid manner is not possible. It is, therefore, the usual practicefirst to dry the wet granular material and then to classify it, but anextra unit operation is required for the drying operation.

' It has now surprisingly been found that notwithstanding theflocculation of the wet granular material in organic liquids otherwisesuitable for sink-float separation operations, the lighter and heavierfractions of the material can be separated from each other if thesink-float classification is carried out under conditions of anartificially increased gravitational field in a cyclone or a likedevice.

It has been known that the sink-float classification of granularmaterials in heavy liquids can be accelerated by the use of centrifuges,cyclones or similar devices, but this knowledge has been limited to thesink-fioat classification of dry materials, which would proceed evenwithout the application of an increased gravitational field though moreslowly. However, it has not been known, nor could it be anticipated,that the increase of the gravitational field makes possible thesink-float classification of wet granular material which cannot normallybe so classified. This new observation on which the invention is based,is surprising and constitutes a departure from accepted beliefs andpractices.

The respective specific gravities of the particles of a wet granularsolid mixture dispersed in an organic liquid have not necessarily thesame relation to each other and to that of the organic liquid as havethose of the same particles it dry, since they may have been modified bythe water or aqueous liquid with which the particles are wetted. Theobservable specific gravity of the wet particles will be called hereintheir apparent specific gravity, irrespective whether it is the same asthat of the particles in the dry state or a different one. It is therule rather than the exception that the several components of an oremixture have different surface affinities for water. Therefore, thesink-float separation of wet mixtures in accordance with this inventioncan in many cases efficaciously classify fractions of markedly difierentapparent specific gravities, which are chemically or mineralogicallydifferent components of an ore mixture, while in the dry state the samecomponents have so nearly equal specific gravities that they cannot beclassified by the sink-float method by means of a water-immiscibleorganic solvent in the absence of water.

The present invention, therefore, consists in a method for thesink-float classification of wet granular mineral materials, wherein adispersion containing the wet material in a flocculated state dispersedin a water-immiscible organic liquid having a specific gravityintermediate between the average apparent specific gravities of thelighter and heavier particles to be separated is subjected to sinkfioatseparation under conditions of a gravitational field increased inrelation to the natural gravitational field of the place of operation.

As a rule the artificial gravitational field applied in accordance withthe invention will be of the order of 5g or higher (where g=9.81 m./sec.

The granular material to which this invention is applicable mayespecially be a mixture of minerals comminuted by any conventionaloperation such as crushing or grinding, or an ore found naturally in afine-grained state.

The average apparent specific gravities of the lighter and heavier floatfractions of wet granular material dispersed in the water-immiscibleorganic solvent in accordance with the invention depend on the intensityof the induced increased gravitational field. It is thus possible tocontrol the composition of the two fractions obtained by theclassification in accordance with the invention by a suitable adjustmentof the intensity of the induced gravitational field.

The invention is applicable, on the one hand, to the classification ofminerals of different specific gravities that are obtained in a wetstate at some stage of the ore dressing process, and on the other handto the classification of dry-ground minerals having equal or nearlyequal specific gravities, if they differ from each other by theirsurface afiinities for water. For the sink-float classification of oremixtures of this kind, the mixture is slurried in an organic liquidimmiscible with water and sufiicient water is added to the dry mixtureor to the organic liquid, or to the mixture of the ore and liquid.

For the production of increased gravitational fields in accordance withthe invention, conventional devices such as cyclones can be employed.

The water-immiscible organic liquid will have to be selected or composedin accordance with the apparent specific gravities of the sink and fioatfractions of each particular mixture. It may be a single substance or amixture of substances. An example of an organic liquid suitable for useby itself or as a component of a mixture is tetrabromoethane. Since thepresence of a water film on the particles to be separated lowers theirabsolute specific gravities, it becomes possible to fractionate wetmixtures all of whose components have a higher specific gravity in thedry state than the water-immiscible organic liquid employed for theseparation.

The invention is illustrated by the following examples to which it isnot limited:

Example 1.Separati0n of chromite (sp. gr. 4.5) from serpentine (sp. gr.2.6)

A chromite ore containing about 35% by weight of chromite, is ground inwater to 20 mesh in order to liberate the minerals. The wet pulp isdrained to a resid ual moisture content of 23-10%. If the resulting wetsand is introduced in tetrabromoethane, it is flocculated and the massof fiocs floats to the surface of the liquid and no separation takesplace. Now the slurry is vigorously mixed by a mechanical stirrer sothat the fiocs are uniformly distributed through the whole body ofliquid and this suspension is fed by gravity or by a pump to a hydrauliccyclone. In the cyclone, separation takes place, and chromite andserpentine report respectively to the underfiow and overflow of thecyclone. In this case, 'both solids have similar surface properties withrespect to water wetting, but widely different specific gravities.

Example 2.-Separati0n of galena (sp. gr. 7.5) from calamine (sp. gr.3.5)

The ore is ground dry to -35 mesh to liberate both minerals. Enoughwater is added to bring the average specific gravity of the wet ore tobelow the specific gravity of 'tetrabromoethane (2.96). For an orecontaining 10% of galena in calamine, this amount of water is of theorder of 11% of the weight of dry ore. The wet ore is slurried intetrabromoethane, the slurry is mixed vigorously and passed through acyclone under a moderate pressure. The galena goes into the underflow,andthe calamine 7 into the overflow.

In this case separation takes place owing to both the wide difierence inspecific gravities and the surface properties of the minerals, ascalamine has a much higher affinity for water than galena. Owing to thcentrifugal force acting. onthe mixture during its passage through the,underflow, while calamine retains the water and since the specificgravity of the wet calamine is lower than thatof tetrabromoethane, thecalamine goes to the overflow.

Example 3.Separati0n of cassiterite from hematite and quartz An alluvialsand (-35 mesh) containing cassiteri-te (sp. gr. 7.4), hematite (sp. gr.4.8), quartz (sp. gr. 2.65) and other gangue minerals of sp. gr; 3 to3.5 is washed to separate fine slimes and the clean sands dewatered'toabout 10% .moisture. The wet sand is slurried in tetrabromoethane andfed to a cyclone by means of a centritugal pump, with a feed pressure ofabout 1 atmosphere above atmospheric pressure. Cassiterite is obtainedin the underflow, while quartz, hematite and the other gangue mineralsare discharged in the overflow.

Example 4.Sepamti0n of a fraction enriched in diamonds from diamondbearing sand A wet sand from South Africa in the size range 10-48 meshcontaining 4.8% of minerals heavier than tetrabromoethane, includinglaterite, staurolite, rutile, leucoxene,

il'menite and diamonds, while the fraction lighter than.

We claim:

1. A method for the sink-float classification of granular solidmaterials composed of at least two fractions which, in a water-wetcondition, have different apparent specific gravities, comprising thesteps of: producing a dispersion of said granular material in awater-wet condition and fiocculated state in an organic liquid having aspecific gravity intermediate between the apparent specific gravities ofsaid fractions, said fractions being incapable of being separated fromeach other in said organic liquid in the natural gravitational field ofthe place of-operation,.subjecting said dispersion to sink-float,separation in a cyclone, under conditions of a gravitational fieldincreased in relation to thenatural gravitational field of the place ofoperation and separately collecting said fractions of different apparentspecific gravity.

2. A method according to claim 1, wherein the sinkfloat separation iscarried out under the action of a gravitational field having anintensity of at least 5g (g=9.81 m./sec.

3. A method according to claim 1, wherein said waterwet condition ofsaid mineral mixture is. initiated in a preceding processing operation.

4. A method according to claim 1, wherein said at least two fractions ofsaid granulanmaterial have, in the dry state, nearly equal specificgravities but, in the wetstate, have sufiiciently difierent apparentspecific gravities to allow their being separated from each other bysaid sinkfloat classification, and wherein said water-wet condition isinitiated during said methodto obtain said different apparent specificgravities.

5. A method according to claim 4, wherein the mineralmixture isintroduced in the wet state into theorganic liquid.

6. A method according to claim 4, wherein first water andthen themineral mixture in the dry state are introduced into the organic liquid.

7. A method according to claim 4, wherein the A dry mineral mixture andwater are introduced concurrently into the organic liquid.

8. A method according to claim 1, wherein the organic liquid consists atleast in part of tetrabromoethane.

References Cited by the Examiner UNITED STATES PATENTS 1,839,117 12/1931Nagelvoort 209l72 2,150,917 3/1939 Foulke 209-172 2,165,607 7/1939 Blow209-472 2,686,592 8/1954 Miller 209+172 X 2,859,917 11/1958 Reerink209-9 X 2,893,557 7/1959 Teuteberg 209-1725 FRANK W. LUTTER, PrimaryExaminer.

1. A METHOD FOR THE SINK-FLOAT CLASSIFICATION OF GRANULAR SOLIDMATERIALS COMPOSED OF AT LEAST TWO FRACTIONS WHICH, IN A WATER-WETCONDITION, HAVE DIFFERENT APPARENT SPECIFIC GRAVITIES, COMPRISING THESTEPS OF: PRODUCING A DISPERSION OF SAID GRANULAR MATERIAL IN AWATER-WET CONDITION AND FLOCCULATED STATE IN AN ORGANIC LIQUID HAVING ASPECIFIC GRAVITY INTERMEDIATE BETWEEN THE APPARENT SPECIFIC GRAVITIES OFSAID FRACTIONS, SAID FRACTIONS BEING INCAPABLE OF BEING SEPARATED FROMEACH OTHER IN SAID ORGANIC LIQUID IN THE NATURAL GRAVITATIONAL FIELD OFTHE PLACE OF OPERATION, SUBJECTING SAID DISPERSION TO SINK-FLOATSEPARATION IN A CYCLONE, UNDER CONDITIONS OF A GRAVITATIONAL FIELDINCREASED IN RELATION TO THE NATURAL GRAVITATIONAL FIELD OF THE PLACE OFOPERATION AND SEPARATELY COLLECTING SAID FRACTIONS OF DIFFERENT APPARENTSPECIFIC GRAVITY.